Arrangement for controlling fluid jets injected into a fluid stream

ABSTRACT

In an air mixing arrangement wherein a primary fluid is introduced through an opening in a wall to be mixed with a secondary fluid flowing along the wall surface, the opening is airfoil shaped with its leading edge being orientated at an attack angle with respect to the secondary fluid flow stream so as to thereby enhance the penetration and dispersion of the primary fluid stream into the secondary fluid stream. The airfoil shaped opening is selectively positioned such that its angle of attack provides the desired lift to optimize the mixing of the two streams for the particular application. In one embodiment, a collar is provided around the opening to prevent the secondary fluid from contacting the surface of the wall during certain conditions of operation. Multiple openings maybe used such as the combination of a larger airfoil shaped opening with a smaller airfoil shaped opened positioned downstream thereof, or a round shaped opening placed upstream of an airfoil shaped opening. Pairs of openings and associated collars maybe placed in symmetric relationship so as to promote mixing in particular applications, and nozzles maybe placed on the inner side of wall to enhance the flow characteristics of the primary fluid.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. Ser. No. 12/142,957, filed Jun.20, 2008, and entitled “Arrangement for Controlling Fluid Jets Injectedinto a Fluid Stream,” which is a divisional application of U.S. Ser. No.11/131,976, filed May 18, 2005, now U.S. Pat. No. 7,415,827. The contentof these applications is incorporated herein by reference it itsentirety.

BACKGROUND OF THE INVENTION

The invention relates generally to the mixing of fluid flow streams and,more particularly to the injection of a primary fluid into a secondaryfluid cross-stream, as found in, but not limited to, jet enginecombustion chambers, jet engine bleed-air discharge nozzles, andjet-engine thrust vectoring nozzles.

A fluid jet injected essentially normally to a fluid cross-stream is animportant phenomenon that is ubiquitous in industrial processesinvolving mixing and dispersion of one fluid stream into another. Forexample, the “jet in cross-flow” phenomenon, as it is commonly called,dictates the efficiency of the mixing process between different gases ina jet combustor, controlling the rates of chemical reactions, NO_(x) andsoot formation, and unwanted temperature non-uniformity of gasesimpinging on the turbine blades.

The jet-in-cross-flow phenomenon is also present at the discharge portof high temperature compressor bleed-air into the fan steam of jetengines, as well as in fuel injector nozzles on afterburners and influidic thrust-vectoring devices.

Herein, we define as “primary fluid” the fluid of the injected jet, andas “secondary fluid” the fluid of the cross-stream. The two maincharacteristics of the jet-in-cross-flow phenomenon are:

-   -   a) the penetration depth of the primary fluid plume into the        secondary fluid stream, and    -   b) the rate of dispersion and mixing of the primary fluid plume        into the secondary fluid stream.

Comprehensive parametric studies of multiple round jets to optimizecrossflow mixing performance have been reported since the early '70s,the most general and applicable to subsonic crossflow mixing in aconfined duct being reported by J. D. Holdeman at NASA (Holdeman, J. D.,“Mixing of Multiple Jets with a Confined Subsonic Crossflow”, Prog.Energy Combust. Sci., Vol. 19, pp. 31-70, 1993.). Those studies, bothnumerical and experimental, developed correlating expression to optimizegas turbine combustor pattern factor. The primary result was that thejet-to-mainstream momentum-flux ratio was the most significant flowvariable and that mixing was similar, independent of orifice diameter,when the orifice spacing and the square-root of the momentum-flux wereinversely proportional. More recent efforts at Darmstadt (Doerr, Th.,Blomeyer, M. M., and Hennecke, D. K., “Optimization of Multiple JetsMixing with a Confined Crossflow”, ASME-96-GT-453, 1996 and Blomeyer, M.M., Krautkremer, B. H., Hennecke, D. K., “Optimization of Mixing forTwo-sided Injection from Opposed Rows of Staggered Jets into a ConfinedCrossflow”, ASME-96-GT-453, 1996.) further studied the optimization ofround jet configurations for gas turbine applications.

Although optimized round jets provide control of pattern factor,reduction of NO_(x) emissions could be attained by more rapid mixing inthe combustion chamber. Since axisymmetric coflow configurations onnon-circular orifices, such as an ellipse, had been shown to increaseentrainment relative to a circular jet (Ho, C-M and Gutmark, E, “VortexInduction and Mass Entrainment in a Small-Aspect-Ration Elliptic Jet”,J. Fluid Mech., Vol. 179, pp. 383-405, 1987 and Gutmark, E. J. andGrinstein, F. F., “Flow Control with Noncircular Jets”, Annual Rev FluidMech., Vol. 11, pp. 239-272, 1999.), similar orifices were consideredfor NO_(x) reduction in crossflow configurations during NASA's HighSpeed Research program in the early '90s. Liscinsky (Liscinsky, D. S.,True, B., and Holdeman, J. D., “Mixing Characteristics of DirectlyOpposed Rows of Jets Injected Normal to a Crossflow in a RectangularDuct”, AIAA-94-0218, 1994.) and Bain (Bain, D. B., Smith, C. E., andHoldeman, J. D., “CFD Assessment of Orifice Aspect Ratio and Mass FlowRation on Jet Mixing in Rectangular Ducts”, AIAA-94-0218, 1994.) usingparallel-sided orifices (squares, rectangles and round-ended slots)launched an investigation to improve upon the mixing performance ofround jets. Optimizing correlations were developed but a significantenhancement in mixing relative to round holes was not achieved. Theslots were also rotated relative to the mainstream to control jettrajectory but mixing enhancement was not observed for optimizedconfigurations. Concurrent investigations in cylindrical ducts wereperformed experimentally and numerically by Sowa (Sowa, W. A., Kroll, J.T., and Samuelsen, G. S., “Optimization of Orifice Geometry forCrossflow Mixing in a Cylindrical Duct”, AIAA-94-0219, 1994.) andnumerically by Oeschle (Oeschle, V. L., Mongia, H. C., and Holdeman, J.D., “An Analytical Study of Jet Mixing in a Cylindrical Duct”,AIAa-93-2043, 1993.) also without significant mixing improvementrelative to circular jets.

Detailed single jet studies of symmetric noncircular orifice shapes incrossflow were also performed in the late 90s (Liscinsky, D. S., True,B., and Holdeman, J. D., “Crossflow Mixing of Noncircular Jets”, Journalof Propulsion and Power, Vol. 12, No. 2, pp. 225-230, 1996 and Zamn,KBMQ, “Effect of Delta Tabs on Mixing and Axis Switching in Jets fromAxisymmetric Nozzles”, AIAA-94-0186, 1994.). These investigations alsoincluded the use of tabs placed at the nozzle exit as vortex generators.Azimuthal non-uniformity at the jet inlet is naturally unstable andintroduces streamwise vorticity which increases entrainment foraxisymmetric flows, however in a crossflow configuration the vorticityfield is dominated by the bending imposed by the mainstream. Thevorticity generated by the initial jet condition was found to beinsignificant and appreciable mixing enhancement relative to a circularjet was not observed.

In summary, a round orifice is the most commonly used shape from whichthe primary fluid emanates, leading to a jet of essentially cylindricalshape in the vicinity of the orifice. This cylindrical shape is rapidlybent by the secondary cross-stream into a plume oriented with thecross-stream direction. Prior-art investigations have been directed atdiscovering improved orifice shapes in the hope of passively improvingeither or both of the plum penetration and dispersion and mixing. Whileslanted slots have provided some reduction in penetration depth, noshapes have been reported that offer significant improvements over theround orifice shape. The lack of a mechanism for the control of plumepenetration depth that is independent of the exit jet velocity is ashortcoming that forces compromises into the design of industrialsystems.

Furthermore, the downstream development of the plume from prior-artnon-circular orifices is similar to that of the plume form the circularorifice. In particular, both circular and non-circular cases generated aplume characterized by a cross-sectional area of kidney-like formcontaining two counter-rotating vortices oriented parallel to thesecondary-fluid stream direction. Far from the plume, the velocityinduced by one vortex of this vortex pair is essentially cancelled bythe other counter-rotating vortex of the pair. Consequently, whenmultiple plumes are present, the counter-rotating vortices produce aweak interaction between neighboring plumes emitted from near-byorifices, leading to relatively weak overall dispersion of the primaryfluid.

It is thus desirable to have an orifice shape that leads to a strongcontrol of primary-fluid plume penetration independent of exit jetvelocity, thus allowing authoritative placement of the jet plume at adesired, predetermined depth into the secondary steam. It is alsodesirable to have an orifice shape leading to a plume containing asingle, rather than a pair, of vortices, that allows strongerinteraction between neighboring plumes.

Objects of the current invention are thus to:

-   -   1) provide a geometry for the primary-fluid orifice that leads        to a strong control authority over the primary fluid plume        penetration depth into the secondary stream, the penetration        control being independent of exit jet velocity, and    -   2) provide a geometry for the primary-fluid orifice that leads        to a primary fluid plume having a single dominant component of        streamwise vorticity, leading to stronger plume-plume        interaction and mixing.

SUMMARY OF THE INVENTION

The orifice from which the primary fluid is emitted is given astreamlined, airfoil-like shape to create (in an extruding fashion) asteamlined jet having a wing-like form in the vicinity of the orifice.The term “streamlined” refers to a body dominated by frictional drag, asopposed to pressure drag. When the wing-like jet is placed at an angleof attack in the secondary fluid cross-stream, a strong tilting forcedevelops on the jet, much like the well known lifting force on a solidwing, causing the jet to bend away from the plane defined by the initialinjection direction and the cross-stream direction. By varying the angleof attack, the magnitude of the lifting force is altered, and thepenetration of the jet is strongly affected. Additionally, the liftforce creates circulatory-flow (i.e. single-sided vorticity) around thejet that maintains itself far downstream of the jet orifice. Both ofthese effects strongly affect the penetration, mixing, and interactionof multiple fluid-wings. For a given airfoil-like orifice shape, thevariation of angle of attack provides a strong control authority overthe jet penetration depth. Since the angle of attack is a geometricquantity, it is independent of the exit velocity of the jet, and, thus,provides a control of jet penetration that is independent of jet exitvelocity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective illustration of one possibleembodiment of the present invention, namely a wing-like orificegeometry.

FIG. 2 is a schematic perspective illustration of a wing-like orificegeometry, and its resulting airflow patterns.

FIG. 3 is a schematic perspective view of the embodiment shown in FIG. 1with an included solid collar attached to the orifice.

FIG. 4 is a schematic perspective illustration of an alternativeembodiment of the present invention, namely a main-wing orifice and anauxiliary flap orifice.

FIG. 5 is a schematic perspective illustration of another embodiment ofthe present invention, namely both circular and wing-like orifices.

FIGS. 6 a-6 c are schematic perspective illustrations of yet anotherembodiment of the present invention, namely a bleed-port attachmentwith:

FIG. 6 a being a top view,

FIG. 6 b being the front view looking along the secondary fluid streamdirection and

FIG. 6 c being a side view.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the first embodiment of the invention as shown in FIGS. 1 and 2, asurface 100 separates an upper region containing a secondary fluidmoving essentially parallel to said plate from a lower region having aprimary fluid at higher pressure than the pressure of the secondaryfluid. The surface 100 could be part of any device that mixescross-streams of fluids, such as combustion chambers, bleed airdischarge nozzles and thrust vectoring nozzles of gas turbine engines.

In a jet engine combustion chamber, the primary air is combustion-freeair injected into a combustion chamber and is referred to as quench airand the secondary air is air having fully or partially burned fuel andis referred to as front-end air.

In a jet engine bleed air discharge nozzle, the primary air iscompressor bleed air and the secondary air is air external to thecompressor (e.g. fan-stream air). In a jet engine thrust vectoringnozzle, the primary air is compressed bleed air and the secondary fluidis jet engine exhaust flow.

The direction of the secondary fluid is indicated by arrow 110. Theplate has at least one orifice 200 allowing fluid communication betweenthe primary and secondary fluids. The orifice 200 comprises aperforation shaped with an airfoil-like form having a leading edge 205,an upper 206 and a lower edge 207 slowly diverging to a point of maximumseparation then slowly converging to a sharp cusp at the trailing edge208, so as to form an airfoil profile of conventional form. Theimaginary line connecting the leading and trailing edge is called thechord, shown at line 209. The orifice is oriented with the leading edgelocated upstream in the secondary fluid flow from the trailing edge andwith the chord aligned with a predetermined angle to the secondary flowdirection, the angle being indicated by the symbol a in FIG. 1. Thepredetermined angle is called the angle of attack, and the combinationof angle of attack and orifice shape, including the camber (camber isthe curvature of the air foil center-line) of the airfoil, determinesthe lift force experienced by the primary fluid particles leaving theorifice, and hence determines the plume penetration. Airfoil shapesdesigned for low Reynolds number flows, as known in the art, are bestsuited. Given an airfoil shape, the angle of attack is chosen to satisfythe needs of each specific engineering application: low angles of attackwhen high penetration is desired, high angles of attack (essentiallybetween 0 and 20 degrees) when low penetration is desired.

Due to the pressure difference between the primary fluid and thesecondary fluid, a jet of primary fluid 210 is emitted from the orifice200 into the secondary fluid cross-stream. The jet of primary fluid 210inherits the airfoil cross-section of the orifice 200 and, consequently,forms a wing-like shape in the vicinity of the orifice 200. Thewing-shaped jet experiences a lateral force shown at arrow 300 which isproportional in strength to said angle of attack. The lateral force 300brings the jet of primary flow substantially perpendicularly away fromthe plane defined by the direction of the primary fluid jet at theorifice and the direction of the secondary cross-stream, therebylowering the overall penetration depth of the jet plume into thesecondary cross-stream.

In the process of developing lift, a circulatory component of fluidmotion, shown at arrows 310 and referred to as “circulation” withinconventional airfoil theory, is established at the base of the jet ofprimary fluid 210. This circulatory motion is convected with the primaryfluid particles and remains with the primary fluid particles (Kelvins'theorem), as shown by arrows 320, even after the jet has lost itswing-like shape and has reoriented itself in the cross-stream direction.The circulatory motion of the primary fluid particles establishes asingle dominant component of streamwise voracity in the jet plume (i.e.avoiding the two counter-rotating vortices produced by conventionalorifice shapes). Thus, the circulating movement of air, as shown by thearrows 310, is dependent on the airfoil shape of the primary fluid flow210 and is generally proportional to the angle of attack α. In turn, theforce, as shown by the arrow 300, is generally proportional to thecirculatory motion 310 and will effect both the penetration depth andthe rate of dispersion for the primary fluid flow 210 into the secondaryfluid flow 110. Generally, a larger attack angle α will result in lesspenetration but greater dispersion. It is thus necessary to choose anappropriate attack angle that will bring about an optimum balance ofpenetration and dispersion. As a general guideline, it is estimated thatan airfoil shaped orifice having an angle of attack of α=0°, provides a30% greater penetration than a round orifice of the same area. Furtherif the same airfoil shaped orifice is presented so as to have an angleof attack of α=10°, then the penetration is estimated to be about half(50%) that of a corresponding round orifice, but with much betterdispersion characteristics. As further guidance, an attack angle in therange of negative 5 to positive 25 degrees is suggested for a jet enginecombustion chamber, and an attack angle of 5 to 15 degrees (as needed toplace the plume away from the nacelle surfaces at downstream locations)is suggested for a jet engine bleed air discharge nozzle.

In reference to FIG. 3, a collar, or solid sleeve 220, is added to theperimeter of orifice 200 to “lift” the orifice off the plane 100.Essentially, the collar gives the orifice an extension into the thirddimension. The collar is beneficial, for example, in those cases whenthe flow through the orifice is reduced to a trickle and the tricklingfluid must avoid contact with the plane 100. Such a case exists, forexample, for the bleed-air port on jet engines, wherein the trickle iscaused by an incomplete closure of the bleed-air valve, and the hottrickling air can damage the nacelle when contacting the nacellesurface.

In another embodiment of the invention as shown in FIG. 4, the orificecomprises a first and second opening. The first opening, shown at 201,forms the “main wing” jet and the second opening, shown at 202, forms anauxiliary flap jet whose role is to increase the efficiency and the liftforce experienced by the main-wing jet, much like a conventionaltrailing edge flap aids the performance of the main wing at lower wingtranslational velocities. Furthermore, the close proximity of themain-wing jet to the flap jet creates a strong interaction between thedownstream plume 330 from the main opening and the downstream plume 340from the flap opening. This interaction leads to increased mixing ofprimary fluid with the secondary fluid.

Another embodiment of the invention is shown in FIG. 5 which relates toa combustor application, wherein it is desired to provide asubstantially increased amount and penetration of primary airflow. Forexample, where the combustor maybe constrained in length and there isn'tsufficient surface to rely on only airfoil shaped orifices, it maybeadvantageous to use a combination of orifice shapes as shown.

In the FIG. 5 embodiment, a surface 100 of a combustor liner separatesan upper region (i.e. the combustion zone) containing a secondary fluidmoving parallel to said plate from a lower region having a primary fluidat higher pressure than the pressure of the secondary fluid. Thesecondary fluid direction is indicated by arrow 110. The plate has apattern of orifices for communication between the primary and secondaryfluid, the pattern comprising a mixture of wing-like orifices andnon-wing-like orifices. Although other shapes could be used, FIG. 5shows the non-wing-like orifices having a circular shape. A part of thispattern is shown in FIG. 5 wherein circular orifices are shown at 400and orifices having a wing-like streamlined cross-section are shown at410. Examples or orifice patterns maybe the alternating rows of circlesand wings, as shown in FIG. 5, or maybe a checkerboard pattern ofcircles and wings (not shown), or other patterns. A jet from circularholes forms a downstream plume of kidney-shaped cross sections, asindicated by 420 that is located away from the plate 100, leaving avolume of secondary fluid below said plume that is not active in themixing of the primary fluid with the secondary fluid. The juxtapositionof circular orifices with wing-like orifices, each at a predeterminedangle of attack, allows a positioning of the downstream plumes from thewing-like orifices 430 below the downstream plumes from the circularorifices 420. This produces mixing between the primary fluid and thesecondary fluid over a greater volume of secondary fluid above theplate. As a further benefit, the pressure-drop between primary andsecondary fluids is less than the pressure drop associated with anorifice pattern consisting of large and small diameter circular holes,wherein the small-diameter holes are used to generate an overall plumedistribution that approximates the distribution generated by theairfoil-shaped orifices.

A further embodiment of the invention is shown in FIGS. 6 a, 6 b and 6 cwherein, in a bleed port attachment application, the authority overplume penetration is used to construct a bleed-port attachment thatpositions and shapes the exhausted bleed-air plume into a desired formand trajectory. A surface 100 (FIG. 6) separates an upper region (e.g.the fan duct) containing a secondary fluid (namely bypass air) movingparallel to said plate from a lower region (e.g. ducts in communicationwith the compressor section of the gas turbine engine) having a primaryfluid (namely core engine air) at higher pressure than the pressure ofthe secondary fluid. The attachment comprises at least two wing-shapedorifices with collars, and preferably four orifices with collarsoriented with an angle of attack with respect to the secondary fluidstream direction, indicated by arrow 110 in FIG. 6 a. The orifices andcollars provide communication between the primary and secondary fluids,and the pressure difference between the primary and secondary fluidsgenerates a jet of primary fluid from each orifice, the jet having anairfoil-like cross section and a wing-like form in the vicinity of eachorifice. When the primary fluid plume must be spread over a wide spacewithin the secondary fluid stream, at least two orifices with collarsare positioned with opposite directed lift directions, such as collars602 and 603 in FIG. 6, such that the corresponding emitted plumes 702and 703 spread laterally away from one another as each plume convects inthe secondary cross-stream flow. The angle of attack of the orificesplus collars 602 and 603 is increased or decreased to reduce or increaseplume penetration into the secondary stream, as desired.

When four orifices with collars are used, the outer two collars 601 and604 are each oriented to give a lift directed in the same direction asthat of the neighboring inner collar, and the outer two collars 601, 604are preferably titled away from the perpendicular direction to plane 100to further assist the lateral displacement of associated plumes 701 and704. When the plumes emitted from the inner orifices 601, 602 penetratefurther into the secondary air stream than the plumes from the outerorifices 601, 604, and an essentially equal penetration of plumes fromall four orifices is desired, the collars of the inner two orifices 602,603 are preferably lower in height than the height of the outer collars601, 604.

When an asymmetric plume development downstream of the bleed port isdesired, the lift direction of same, or all, of the orifices and collarsmaybe oriented toward the desired side of the bleed port (asymmetricbleed-port attachment not shown).

Guide vanes 620 extend from the bleed-port attachment into the pipingfeeding the bleed-port to partition the primary fluid flow into partsappropriate for each orifice. Furthermore, the guide vanes help preventundesired unsteadiness in the fluid emitted from each orifice.

In addition to the advantages and benefits of the present invention asdiscussed hereinabove, the reduction in NO_(x) gas resulting fromlowered operating temperatures should be mentioned. In this regard, itshould be recognized that, in a jet engine combustion chamber, thesecondary fluid contains combustible fuel as it approaches and passesaround the plume being introduced by the primary fluid. When this plumeis substantially round, as will be the case for round orifices, therewill be a substantial wake created on the downstream side of the primaryfluid plume. The entrained fuel tends to remain within that wake and itstemperature is, accordingly, caused to rise to the point where NO_(x)gases are formed. This is to be contrasted with the rather sharptrailing edge of a primary fluid plume resulting from an airfoil shapedorifice. Here, there is very little, if any, wake created at thetrailing edge and therefore the fuel is not trapped in this area, butcontinues to flow downstream and remain at temperatures that are notlikely to cause NO_(x) formation.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawing, itwill be understood by one skilled in the art that various changes indetail maybe effected therein without departing from the scope of theinvention as defined by the claims.

We claim:
 1. An apparatus for injecting a primary fluid flow stream intothe flow stream of a secondary fluid, said apparatus comprising: a wallmember defining a boundary for the flow of the secondary fluid in afirst direction over its one surface, said wall member having at leastone opening formed therein for the flow of the primary fluid therethrough in a second direction so as to be mixed with the secondaryfluid, wherein said at least one opening being shaped in the form of anairfoil and orientated at an angle of attack, a, with respect to saidfirst direction, wherein said apparatus comprises a jet engine thrustvectoring nozzle, and wherein said primary fluid is compressed bleed airand said secondary fluid is jet engine exhaust flow.
 2. An apparatusaccording to claim 1, wherein said angle of attack is in the range ofbetween approximately minus 5 to 25 degrees.
 3. An apparatus accordingto claim 1, wherein said at least one opening comprises a plurality ofairfoil shaped openings.
 4. An apparatus for mixing a primary fluidstream with a secondary fluid stream flowing in a first directioncomprising: a wall defining a boundary for said secondary fluid stream,said wall having at least one airfoil shaped opening; and means forproviding a flow of said primary fluid in a second direction throughsaid airfoil shaped opening for mixing with said secondary fluid stream,wherein said apparatus comprises a jet engine thrust vectoring nozzle;and wherein said primary fluid is compressed bleed air and saidsecondary fluid is jet engine exhaust flow.
 5. An apparatus according toclaim 4, wherein said second direction is substantially normal to saidfirst direction.
 6. An apparatus according to claim 4, wherein saidairfoil shaped opening has a leading edge and a trailing edge and isorientated at an angle of attack, or, with respect to said firstdirection.